Selector switching system



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SELECTOR SWITCHING SYSTEM Filed Feb. 23, 1946 10 Sheets-Sheet 9 SON OU SECONDARY CONTROLLER SCA TRUNK-TEST RELAYS 22711727271": Ja/m [BE/[E222 H I GH RESISTANCE Patented July 10, 1951 UNITED STATES PATENT OFFICE SELECTOR SWITCHING- SYSTEM John l I. Bellamy,

log i Switchbo Brookfield, Ill., assignor to Kelard and Supply Company, Chicago, Ill., acorporation of Illinois ApplicationFebruary 23, 1946, Serial No. 649,595

1 25 Claims;

GENERAL DESCRIPTION This application is a continuation in part of my prior application for Selector Switching Systems, Serial No. 531,949, filed April 20, 1944, now Patent No. 2,400,530, issued May 21, 1946.

Features of improvement over my above-noted prior application include the fol-lowing:

1. A considerable reduction in group-controller equipment, and in the relay equipment required at any of the primary or secondary subgroups for individualizing any such subgroup with any group controller, is eifected by arranging any group controller to handle calls to any one of a plurality of numerical groups of outgoing trunk lines. The group controllers are accordingly substantially reduced in number (from ten to two in the illustrated example). In the improved groupcontroller arrangement, suitable relay apparatus is provided for effectively associating any seized group controller with any outgoing numerical trunk group over which it may preside, thereby adapting it for operation accordingly.

2. As a current-saving feature, suitable relay arrangements are provided for energizing the test relays of idle outgoing trunks by numerical groups, the energization of any such relays of any numerical group, being dependent upon the receipt of a call for such numerical group.

3. In order to avoid the possibility of false operation of the select magnets at the primary and secondary subgroups over what, may be termed sneak circuit paths, such as may exist with the multipled magnet-wire interconnections within the spread cable in the first embodiment shown in my previously-noted prior application, as when one or more current-supply fuses are out, an improved circuit arrangement is provided for operating in series all primary and secondary select magnets which are to operate incidental to the completion of a single connection, and for operating all such select magnets from a single fused source of operating current. This arrangement includes circuit apparatus for'individualizing' a group controller with common magnet conductors at the primary subgroup at which the call being handled is-waiting; andwith common magnet conductors at the secondary subgroup through which the waiting, call is topass.

4. Each group controlleriincludes' an efiicient' simplified relay arrangement for allotting first choice to the several secondary subgroups in succession, whereby the trafiic' is offered to them in generally uniform proportions.

Other objects and features of the invention, for the most part incidental to the features of improvement enumerated above, will appearupon afurther perusal of the specification.

It' has been chosen to illustrate this invention in connection with a generally similar to that disclosedin Figs. 1 to 8 THE DRAWINGS Fig. 1 is a call-through diagram showing. a

connection completed from the calling line to a called line by way of' a selector stage employing a selector system according to the, invention;

Fig. 2 is a schematic trunking diagram illustrating the general arrangement of thev improved selector, system;

Figs. 3 to 9. arecircuit drawings of portions of the equipment indicated. in Fig. 2;

Fig. 10 shows the way Figs. 3 to 9am intended to be assembled.

As disclosed, the selector system employstwenty-point, three-wire switches generally as dis closed in my application for. Automatic Telephone SwitchesSeriallNo. 524,816, filed March 1 1944, now U. S. Patent No. 2,490,665,. granted December 6, 1949 butsomewhat modified as will be hereinafter described, I

THE PRIMARY-.SECONDARY ARRANGEMENT primary subgroups of switches, A to I, are indicated and nine secondary subgroups of switches A to I, are indicated. Primarysubgroups C to H and secondary subgroups C to Hare omitted from the drawing for the sake of simplicity and to conserve drawing space. Since eachsubgroup of primary or secondary switches may have access to twenty selector links, the number of selector links is twenty times the number of primary or secondary subgroups. In the illustrative example, the nine primary and nine secondary subgroups (A to I) provide for a total ofselector links. In this arrangement, the number of selector links may vary from forty to four hundred, according to the trafiic to be carried by the primary-secondary group of switches, for the selector switching stage at the selector stage, and

number of subgroups can vary from two to twenty.

The number of primary or secondary switches in a subgroup has more or less arbitrarily been set at fifteen. By this arrangement, only fifteen of the twenty selector links served by a primary or a secondary subgroup can be in use at the same time, whereby the selector links are operated at a very low traffic density and a consequently low lost-call rate, which is in keeping with their comparative low cost.

In Fig. 2, the primary switches are represented by horizontal lines PA! to PAW for primary subgroup A, PBS to PBI for primary'subgroup B, and PI! to P115 for primary subgroup I. The secondary switches are represented by horizontal lines SA! to SALE for secondary subgroups A, SB! to SBI5 for secondary subgroup B, and SII to S115 for secondary subgroup I. The vertical lines extending across a subgroup represent the twenty link outlets of the subgroup by way of the twenty contact sets of any switch in such subgroup. The common outlet (or inlet) terminals of a subgroup are shown at the top, numbered l 1020. A few of the 180 selector links are shown interconnecting primary-subgroup terminals with secondary-subgroup terminals.

The nine primary subgroups, A to I, of Fig. 2, with fifteen primary trunks each serve as terminating points for 135 incoming trunks IT! to ITI35. Similarly, the nine secondary subgroups serve as starting points ,for 135 outgoing trunks CT! to OTI35. The selector links are spread between the primary and secondary subgroups on the basis of each primary subgroup having access to at least one link extending to each secondary subgroup, and vice versa. When only two primary and two secondary subgroups are required, half the links from any primary subgroup extend to one secondary subgroup, the remaining half to the other. When twenty primary and twenty secondary subgroups are required, the twenty links from any primary subgroup extend respectively to the twenty secondary subgroups. For each intermediate number of primary and secondary subgroups, a separate spreading arrangement may be employed, as will be readily understood. For nine primary and nine secondary subgroups, as assumed herein,

each primary subgroup has access to three links 1 extending to each of two of the secondary subgroups, and two links extending to each of the other seven secondary subgroups.

The following table shows the general spread arrangement for each number of primary and secondary subgroups from two to twenty:

Subgroup To The Secondary Subgroups No. of Subgroups to each 7 each to two; 6 to one 5 to each .4 to each 4 each to two; 3 each to four 3 each to six; 2 to one} 3 each to four; 2 each to four 3 each to two; 2 each to seven 2 to each 2 each to nine; 1 each to two 2 each to eight; 1 each to four 2 each to seven; 1 each to six 2 each to six; 1 each to eight 2 each to five; 1 each to ten 2 each to four; 1 each to twelve 2 each to three; 1 each to fourteen 2 each to two; 1 each to sixteen 2 to one; 1 each to eighteen 1 to each In carrying out any of the general spread arrangements indicated in Table 1, an orderly specific arrangement may be adopted wherein the selector link extending from any primary subgroup terminal extends to the correspondingly numbered (1 to 20) terminal in the desired secondary subgroup, and wherein the spread of selector links extending from any primary subgroup begins with the corresponding secondary subgroup.

The following table gives the specific arrangement chosen and considered preferable for the system of Fig. 2, wherein 180 selector links interconnect nine primary and secondary subgroups A to I.

TABLE 2 From To From To From To Sel. Sel. Sel

- Prl. Sec. Pri. Sec. Prl. Sec. Lmk Term. Term. Lmk Term. Term. Term. Term.

A1 111 21... B1 B1 41..- 01 G1 A2 A2 22.-- B2 B2 42... 02 G2 A3 a B3 12 43... c3 c3 .44 B4 24... B4 04 44... 04 F4 A5 B5 B5 05 45... 05 D5 .10 0 20..- B0 40-.. 00 1 A7 07 B7 D7 47-.. 07 E7 8..... A8 29... B8 1 48... 08 E8 .49 D9 29..- B9 B9 49... 09 F9 10.... A10 )L1( 30... B10 112 50... C10 F10 E11 31..- B11 F11 51..- 011 GT1 F13 33--- B13 G13 53.-. C13 H13 H17 57... B17 117 57... 017 Hi 119 39.-. B19 .119 59... C19 B19 20.... A20 1 2 0 40--. B20 0 00--. 020 B20 01...- D1 D1 51... El E1 101.- F1 F1 02...- D2 D2 52.-- E2 E2 102.. F2 F2 03.-.. D3 83... E3 2 103. F3 F3 04..- D4 B4 84--- F4 F4 104. F4 51 0 50... E6 13 100.. F0 E 07.... D7 F7 87... E7 G7 107.. F7 H7 68.... D8 11 88... E8 a 109.. F8 119 09.... D9 G9 99... E9 H0 109-. F9 19 70.... D10 G10 90... E10 HE 110.. F10 1g) 71...- D11 H11 91... E11 111 111.- F11 1111 72..-. D12 1 11 2 92.-- B12 11 2 112.- F12 .5 73.... D13 113 93.-. E13 113 113.- F13 1113 74.... D14 114 94... 214 gr 114.. F14 4 75.... D15 A15 95... B15 B15 115-. F15 015 70.... D16 9 90..- B10 10 110-- F10 9 g 77.-.. D17 B17 97--- E17 017 117-- F17 D11 75 D18 13g 98... E15 o 11 a 11s.. F12 122 79.... D19 C19 99... E19 D19 119.. F19 E19 80.. D20 92 100.- E20 D 20 120.- F20 1 1 121-.. G1 G1 141.- H1 H1 101.- 11 I1 122... G2 G2 142-- H2 H2 102.. 12 I2 123... G3 g5 143-. H3 131 103.- 13 i1 124... G4 H4 144.- H4 14 104.. 14 A4 125... G5 H5 145.- H5 15 105.- I5 .15 120... G0 Q 140.- H6 10 150.. 10 51 127..- G7 17 147.- H7 A7 107.- 17 B7 128... G8 s 1451.. H8 g 108.. 18 11g 129... G9 119 149.- H9 B9 109.. 19 09 1210... G10 .31 H10 B ll 170.. I10 (29 131--- G11 B11 151.. H11 011 171-- 111 D11 192-.- G12 B12 152.- H12 912 172.- 112 1112 1321... G13 013 155.. H13 D13 173.. 113 E13 1214... G14 14 154.. H14 34 174.- 114 B 14 135..- G15 D15 H15 E15 I15 F15 190... G10 1 1 150.. H10 112 170.- 110 F 1 0 137-.. G17 E17 157.. H17 F17 177.- I17 G17 1911... G18 E m 15s.. H18 1335 17s-. 119 g 139... G19 F19 159.- H19 G19 179.- I19 H19 140..- G20 F20 100-- H20 9g) 180.. 120 1122 NUMERICAL Gnourmc or Ourcomc TRUNKS ing? to a separate destination, usually a separate group" of calledilines. Each'su'chseparate group of outgoing trunks may be designated a numerioa-l group', in that. each group bears a separate number, or digit, designation. It is assumed: that the outgoing trunks indicated in Fig.2 are divide'd into ten numerical groups of which groups I, 2', and are represented respectively by cables 2, 2l2, and 220.

For convenience in grouping; the outgoing trunks OTI to OTI35 may bepassed through an intermediate distributing frame indicated at IDF, across which each trunk may be carried by a separatejumper connection. The preferred as-- sign'ment of outgoing trunks to the numerical groups is such that each numerical group contains as nearly as possible the same number of trunks: from each secondary subgroup; an idealrarely obtaining in practice.

The 135' outgoing trunks OT! to OTl'35='pro'-- vide' an. average of thirteenandone-half trunks for each of the ten outgoing numerical" groups I to" 0". Some numerical groups may contain only ten trunks, or fewer, while other numerical groups may contain" twenty trunks or more; all depending upon the t'rafiic requirements:

THE GROUP-CONTROLLER ARRANGEMENT groups. The ten group controllers used in the,

similar embodiment of my previously noted rior application- Serial No. 531,949, are thus. reduced to two.- This reduction in the number of group.

controllers is based on mathematical calculations, not necessary to reproduce here, which show that a single group controller can handle, on a oneat-a-time basis, at least the numberof calls which can be expected to be directed to'five numerical groups served by a selector switching stage of the size specifically illustrated. Selector switching stages considerably smaller than" the one specifically illustrated may be served entirely by a single group controller, while still larger selector switching stages may requirethree or more group controllers, the number required being calculated from the number of calls expected to pass through the selector switching stage during. the so-called busy hour.

The previously-noted calculations indicate that a single group controller can handle up to three thousand calls during the busy hour with not more than one lost call in a thousand due to unavailability of a group controller, provided theoperate cycle of a group controller. does not exmed .1 second, and provided the start relays of the selectors (see relay 304, Fig. 3) are so adjusted that .25- secondv of the usual interdigitl interval remains after the operation of any such start relay. Each group controller is arranged to direct any primary switchin any subgroup to extend. a connection to any outgoing trunk in any one of the numerical groups over which it presides, by way-of a selector link and the concerned secondary switch. Any operating group" controller is assisted inselection of an idle outgoing-trunk by-one or another of the nine sec'-' ondary controllers 56A to SCI; according to the secondary: subgroup: through:-.. which-connection with-an: idle-trunk inthe called numerical group islocated. Thesecondary controllers are con-. nected with the. group-controllers through the nine cables HI to H9. Since each secondary subgrouphas its own secondary controller,- each secondary subgroupis able to act as a unit independent of the others;

THE .SELECTORS trol functions, and for-transmittingimpulses toa register device, through which selection is made of one or another often so-called dial leads, one for each-separate digit value employed to direct a call through the selector stage. of ten digit values is employed for each of the ten numerical groups 'I to 0 of outgoing trunks.

Each subgroup of selectors is provided with two connecting relays, such as relays 4 M and402 o1 subgroup A, to which the dial leads DLlto DLI) of that selector'subgroup extend; in two groups of live each. Through the selection and operation of one oranother of the relays 40f and 40!, connection is made with the corresponding one of the group controller'sGcl and'GC2, by way of a local'c'able'such asll' and the concerned group cable 421 and 42?, whereby the requisite number of connections is made to the group controller to enable the latter: to control the extension of the connection to an idle trunkiin the called numerical group;

Each selector subgroup is providedwith its own set of dial leads, such as dial leads DLI to DLD for selector subgroup A. There is one such dial lead for each outgoing numerical group. Dial leads DLI to DL5 of selectorv subgroup .A all extend to the same group-controller relay 4!". Similarly, leads DL6. to DLI] all extend to the same group-controller relay- 402. Individual series relays 43f to 440 are employed to distinguish between the five dial leads extending to a single relay suchas 4M. and. 402, whereby either of the group controllers GCL and G02 is in-- act asa unit. independent ott-he-othersp selectors-,1 together with. thirteen: intermediate A Separate one selectors, form' selector subgroup A of Fig. 2. Cable 350 contains the fifteen selector multiples SMI to SMIS, which interconnect the selectors of selector subgroup A with the respective corresponding switches of primary subgroup A, the first and last of these multiples being shown in Figs. 3 and 5. Fig. 3 also shows dial leads DLl to DLfl which are multiply connected to the contacts of the registers such as R309, a separate such register being provided for each selector.

Figure 4 Fig. 4 shows the group-controller connecting relays MI and 402 to which the dial leads DLI to DLD of selector subgroup A extend, together with group relays RBI to 440, connected respectively in series with the dial leads. Either of relays 4B! and 492, when operated over any associated dial lead, from any selector in selector subgroup A, operates to interconnect conductors 3 IO, (N l, and the conductors in subgroup-A cable 450, to conductors in the associated one of the cables HI and 422, extending respectively to group controllers GCI and G02.

Relays 435 to Mill serve respectively to ground conductors GI to G to notify the concerned seized group controller of the identity of the group being called.

Figures and 6 Fig. 5 shows the circuit arrangement of primary subgroup A of Fig. 2, primary switches PAI and PAH: being shown. The intermediate primary switches of this subgroup are omitted to conserve drawing space. Primary switch PAI, for example, contains twelve selective stackups of contacts I to l2 (stackups 3 to 9 are omitted to conserve drawing space) and an ofi-normal stackup ON. The arrangement for selecting and operating the stackups oi? contacts may be generally as shown and described in my previously identified prior application Serial No. 524,816, except that twelve selective stackups of contacts are provided for each switch, and twelve select magnets are provided, one for each of the stackups of contacts I to l2. The select magnets for stackups I, 2, H], H, and 12 are magnets :52], 522, 530, 53!, and 5'52. Select magnet 531, or 532 associated respectively with stackups l i and i2 of any primary switch of the subgroup, is operated (along with one of the magnets 52l to 5%) depending upon whether the upper contact set or the lower contact set of an operated stackup I to I!) is to be effective.

For the operation, and maintenance, of the selected combination of stackups, each switch is provided with a hold magnet (Bill for switch PAl, and 515 for switch PAI5).

The off-normal stackup ON of any of the switches is not a selective stackup, being operated each time the corresponding hold magnet, such as 581, is energized, irrespective of what stackup selection has been accomplished.

Each primary and each secondary subgroup of switches is preferably separately fused, and is provided with its own set of select magnets such as 52! to 532, and with its own set of six selecting shafts (not shown), whereby each such subgroup is capable of operating as a unitindependent of the other subgroups.

Fig. 6 is a drawing corresponding generally to Fig; 5, but showing secondary subgroup A instead of primary subgroup A. Here again, only the first and fifteenth switches are shown, and stackups 3 to 9 are omitted. Magnets 62l to 632 correspond respectively to magnets 52! to 532; and hold magnets SUI and 615 correspond respectively to magnets 50! and H5.

Fig. 5 shows the three-conductor incoming trunks ITI and IT? terminating respectively in primary switches PA! and PAI5, and Fig. 6 shows the three-conductor outgoing trunks OTI and OTl5 extending respectively from secondary switches SA! and SAI5.

Assuming the primary and secondary subgroups to be mounted in superposed relation as indicated in Fig. 2, spread cable 600 extends vertically between them, and has pairs of lateral branches for the respective primary and secondary subgroups. Branches PAI and PAZ are the lateral branches for primary subgroup A, and branches SM and SA2 are those for secondary subgroup A. This spread cable contains conductor sets comprising the selector links interconnecting the subgroups of primary and secondary switches according to Table 2, appearing hereinbefore. Each selector link (such as SLl to SLZB, extending from primary subgroup A) includes four conductors. These comprise a magnet conductor such as Ml to M20 in branch PA2, and the usual tip, ring, and sleeve conductors T, R, and S in branch PAI The magnet conductor, such as MI to M20, in any selector link is the conductor over which the one of the ten select magnets such as 52l to 530 in the primary subgroup is operated in series with the corresponding select magnet in the secondary subgroup to which such link extends.

The six contact pairs in stackups I to [0 of any switch comprise an upper set of three and a lower set of three, each switch having ten upper sets and ten lower sets. The upper sets represent terminal sets I to 10, respectively, of the subgroup, while the lower sets represent terminal sets I I to 29, respectively. Stackup ll of any switch is operable to render sets I to II) efiective, while stackup I2 is operable to render sets i l to 20 effective.

Figure 7 Fig. 7 shows the circuit arrangement at group controller GCI of Fig. 2, the circuit arrangement at group controller G62 being generally similar.

Group controller GCI includes start and test relays 1M and H32, a pair of busy relays I03 and 10 a preference allotter comprising relays H8 to I30, and twenty-seven link-test relays IA to 31. The link-test relays are assigned in subgroups of three to test the links extending from a calling primary subgroup to the respective secondary subgroups. This is in accordance with preceding Table 2, wherein it will be noted that not more than three selector links extend from any primary subgroup to any secondary subgroup. Relays IA to 3A are assigned to links extending from any calling primary subgroup to secondary subgroup A; relays. {B to 3B are assigned to links extending to secondary subgroup B; and so on, to relays II to 31, which are assigned to links extending from any calling primary subgroup to secondary subgroup I.

Group controller GUI is connected with selector subgroups A to I by the conductors in cable 421 incoming to Fig. 7, part I, from Fig. 4. Group controller GCI is directly interconnected with the nine secondary controllers (SCA to SCI), by conductor pairs GClA, GCl-B, and so forth to GCII, lying respectively in cables Hi to H9;

These cables carry similar conductor pairs to the secondary controllers from group controller G02. These latter conductor pairs (not shown in Fig. '7) may be termed GCZ-A, GC2-B, and so forth to group controller GCZ is essence 'GGZ I, so as toindica'te the 'group controller at which they originate, and the secondary controller to which they extend. Any one of the con- These pairs'are labeled Ato 'I,--and-exten'd-downwardly from Fig. 7 to the grouping relays shown in Fig. 8. It will be understood, of course, that provided with similar pairs of conductors. Eachsuch'pair is associated with the corresponding secondary branch of v the test chain, and comprises conductors IN and OUT. They represent respectively the test conductor leading into the secondary subgroup and the return test conductor eifec'ti-vely leading back out of the secondary subgroup when such subgroup contains no idle trunk-assigned to the numerical group being currently called through the group controller.

Figure 8 Fig. 8 shows grouping relays '8 to 845, corresponding respectively to outgoing numerical groups I to 5. These relays are interposed between the secondary subgroups and the conductor pairs A to I of group controller G'C'l, Fig.

7, to enable such group controller to be used to control the completion of a connection to any one of the first five outgoing numerical group of trunks. Grouping relays 14! to 145 are operated respectively overconductors GI to "G5 in cable 42L controlled respectively by the five relays at any selector subgroup corresponding to relays 43! to 435 at selector subgroup A, Fig. 4, according to the destination ofthe call occasioning the seizure of the-group controller. Itwill be understood that five grouping relays similar to "I to 145-are associated with the othergroup controller and are controlled respectively over group conductors G6 to G0 in cable 422 of Fig. 4.

When operated, any one of the relays- 14l to I45 connects conductor pairs A to I of the group controller of Fig. 7 respectively to its corresponding pairs of IN and OUT test conductors extending to the secondary controllers, thereby adapting the group controller for the operation in handling a call to outgoing numerical groups assigned to it.

Fig. 8 shows also grouping relays 85! to 855, operated respectively over group conductors GI to G5. When operated, any such relay applies ground potential, through conductors in cables H I to 1l9, toa terminal of each of the secondary test relays associated with an outgoing trunk assigned to the corresponding outgoing numerical group, whereby any such test relay (see for example relays TI to T15, Fig. 9, part 1) is operated only when a call is directed to the concerned outgoing numerical group.

Fig. 8 shows also common test start relay 889 which appliesstarting ground individually to the secondary controllers, thereby avoiding the possibility of confused operation of relays such as 82! in the event of an open fuse at any one of the secondary subgroups.

Figure 9 Fig. 9, comprising parts 1 and 2, shows secondthe concerned one of the five "ary-c'ontroller 80A of Fig. 2,-the'other secondary controller's being similar. Relays Ti to Tl5 are test relays corresponding "respectively to the fifteentrunksfiOTl to OTIS, outgoing from the associated secondary subgroup A. The interconnection between the outgoing trunks and relays TI to 'Tl'5 isthrough conductors S! to SIS inca'ble 650,and'by way of contacts of connect- "ing'relay era, when operated.

Relays Sill to'QilZ are group-controller relays "assigned respectively to group controllers GCI and GC'Z. Each such group-controller relay is operable only from the correspondinggroup controller, and then only if the "secondary "controller is "idle; "Upon'the operation of either group- 'controllert'relay "9'01 or 902, operations occur to "station B will now be'des'cribed.

When the receiver (not shown) is removed at substation A, a direct-current bridge is established acrossth'e tip and ring conductors of the "associated line, operating line'relay Nil through contacts or cutoff relay Hi2 to cause finder action 'to'oc'cur at the'ass'ociated finder stage. As a result of this finder action, the tip, ring, and sleeve conductors of the calling line are extended in any desired manner to an idle trunk line such as trunk line ITl incoming to the selector stage. ITLit'may bep'o'inted out, is shown also in Fig. '5, incoming to the primary switch PAi. The "trunk line IT! is normally marked idle by an idle-indicating battery potential applied to the sleeve conductor S thereof by way of contacts of release relay 302 and contacts'in s'tackup ON of the associated primary switch PA], the connection including the illustrated current-limiting resistor.

When the finder-stage extension has been made, line relay Sill associated with trunk IT! (being a relay of selector SEL-Al, Fig. 3) operates over the calling line, causing operation of the associated release relay 392. Relay 3&2 disconnects the normally applied idle-indicating battery potential and substitutes ground potential to maintain, in the usual manner, the connection established through the finder stage,

closing an operating circuit for cutoif relay H32.

.relay 30! causes a selecting operation to occur in a manner to be explained subsequently inconnection with Fig. 3. Upon the termination of the dialing of this digit, operations occur to test the selector links such as SLI accessible to primary switch PM, and to test the trunks extending from the secondary switches such as SAI to the connector-stage group containing the desired called line. The testing of sleeve conductor S of selector link SLI occurs over the illustrated downward extension Si thereof, while the testing of outgoing trunk OTI is performed over its sleeve conductor S, over the indicated downward extension SI, connected therewith through the operating winding of hold magnet 601 of the associated secondary switch SAI Assuming that the testing operation determines that selector link SLI and outgoing trunk OTI are both idle, and are to be used for the connection, selecting operations occur as will be subsequently described to cause selector link SLI to be selected by mechanism common to the primary switch PM and other switches in the same primary subgroup. Similar selecting operations occur in the mechanism common to secondary switch SA! and other switches in the same secondary subgroup. When these selecting operations have been performed, the conductor labeled SW, and extending downwardly from the lefthand winding of hold magnet 50!, is temporarily grounded, causing magnet 5M to operate to close the associated contact stackups H and l, thereby extending the tip, ring, and sleeve conductors of incoming trunk ITI respectively to the corresponding conductors of selector link SL1. At the same time, ground potential is temporarily applied to the lead Sl extending downwardly from the right-hand winding of hold magnet 6M, thereby closing an operating circuit for this magnet over the sleeve conductor of trunk OTI to bat tery through contacts of release relay HI and the associated current-limiting resistor. Magnet 68! thereupon operates to close its contact stackups i and H, further extending the connection to the tip, ring, and sleeve conductors of outgoing trunk OTI. Thereupon, line relay H (being a portion of the connector-stage equipment to which trunk OTI extends) operates over the calling line and causes release relay III to operate. The latter relay disconnects the normally applied source of idle-indicating battery potential from sleeve conductor S of trunk OTI and substitutes a holding ground potential.

Stackups ON in switches PAI and SA! are actuated by the said operation of their respective magnets M and 6M. Ground potential on the sleeve conductor of the extended connection is eifective to energize the hold winding of magnet Gill through the associated oft-normal contacts.

Similarly, the hold winding of magnet 50! is energized through its associated off-normal contacts over the sleeve conductor. The cit-normal stackup ON of switch PAI also disconnects the associated line relay 3!! l following which relays 30! and 362 restore. The holding ground potential is subsequently maintained by release relay I, through which magnets and 5M, and cutoff relay I02, are maintained operated, along with any holding magnets or relays (not shown) required at the finder stage.

The temporary circuits closed to select and operate the hold magnets 50] and Bill are shortly opened, leaving the connection maintained by the above-noted holding ground potential on the sleeve conductor thereof. The lower pair of contacts in stackup ON of switch PA! prevents reapplication of the normally applied source of idleindicating battery potential, upon the restoration windings of line relay H0.

-.of-release relay 302, thereby avoiding unnecessary current drain.

relay H0 responding to the further dialing to deliver the required local series of impulses.

When the connection is completed to the called line, ground potential is applied to the sleeve conductor thereof, operating cutoff relay l02'to disconnect the associated line-relay bridge.

After the called subscriber has been signalled in the usual manner and has answered, the tall:- ing connection is completed as indicated by the dotted connections. Talking current is supplied to thecalled line through back-bridge relay H2, being supplied to the calling line through the The voice currents pass through the usual talking condensers H3 and H4.

When the conversation has been completed, the replacing of the receiver at the calling substation permits line relay H0 to restore, followed shortly by the restoration of release relay l I I. When the latter relay restores, it removes the holding ground potential from the sleeve conductor of the established connection, whereupon magnets Bill and 5M and cutofi relay Hi2 restore, along with any holding magnets or cutoff relays at the finder stage, immediately clearing out the connection between the calling line and trunk OTI.

B. FIGURES 3 To 9 B1. Seizure of incoming trunk; IT1

Referring now to Figs. 3 to 9, the operations involved in extending a connection through the selector switching system at the selector stage of Fig. 2 will be further given in detail.

When incoming trunk IT! (Fig. 5) is idle, an

idle-indicating battery potential is impressed on its sleeve conductor S as follows: from the ungrounded pole of the exchange battery, through the illustrated current-limiting resistor and normally closed make-busy contacts associated with off-normal stackup ON of switch PAI, a pair of normally closed contacts in the said stackup, guard conductor G in selector multiple SMI, back contact of armature l of release relay 302 of selector SEL-Al, and thence, over conductor S in selector multiple SMI, to sleeve conductor S of incoming trunk I'Il.

Upon seizure of incoming trunk ITI, the bridging of the calling line across the tip and ring conductors T and R thereof closes an energizing circuit, through normally closed contacts in the associated stackup ON, and conductors T and R of SMI, for the windings of line relay 39!. Line relay 39! thereupon operates, followed by the operation of slow-restoring release relay 302. At its armature l, relay 302 disconnects the incoming sleeve conductor from the normally connected source of idle-indicating potential and substitutes a holding ground potential therefor, through which the partially established connection is temporarily maintained. At its armature 4, relay 382 closes a circuit, through contacts of busy relay 303, for hold winding H of magnet 35! of register 300; at its armature 5, it prepares an impulse circuit for operate winding 0 of register 300; at its armature 2, it applies ground potential to the common start lead ST to start the common tone apparatus (notshown); and, at its armature 3, it closes a .connection between the associated ring conductor R and the common dialtone lead DI', by way of condenser 396. A dialtone signal is thereby transmitted back to the calling substation to inform the calling subscriber that he may begin to dial the digits in the desired number.

B2. Dialing At this point, it should be noted that the register R360 is of the construction and operation disclosed in my prior application, Serial N 0. 493,312, filed July 2, 1943, now U. S.'Patent No. Re. 23, 089. Briefly, the construction is such that energization of hold winding H of magnet 35! produces no immediate eilect; transmission of the first impulse to winding E1 of magnet 35! causes simultaneous closure of oiT-normal contacts ON and of contacts I of the register; transmission of the second impulse causes separation of contacts I and the closure of contacts 2; transmission of the third impulse causes separation of contacts 2 and the closure of contacts 3, and so forth.

Upon the dialing of the first digit in the desired number, line relay 3! is momentarily restored a number of times corresponding to the digit value (1 to thereof. Upon each restoration of line relay 30!, release relay S02 is opencircuited. Being slow-restoring, release relay 302 remains operated notwithstanding.

Upon each momentary restoration of line relay 3M, an impulse is transmitted to winding 0 of magnet 35!. As above noted, contacts ON and I of register R300 close responsive to this impulse. Off-normal contacts ON remain closed thereafter, but delivery of a second impulse causes contacts I to open and contacts 2 to close. Each succeeding impulse causes the last closed pair of contacts to open and the next succeeding pair to close.

At the termination of the series of impulses, the one of contact pairs I to 0 of REM! which corresponds to the value of the dialed digit is in closed condition, the others being open.

In the present example, it may be assumed that the first digit dialed is the digit 1, in which case contacts ON and I of the register R300 are in closed condition at the termination of the dialing of the digit.

B3. Termination of dialing Following closure of off-normal contacts ON of register 308, each reoperation of line relay 3M completes a circuit for start relay 304. Relay 364 is so designed and adjusted that it does not operate responsive to the momentary impulses it receives during the remaining portion of the dialing of the digit.

When line relay SUI comes to rest in an operated condition at the end of the dialing of the digit, start relay 3M operates fairly promptly. At its armature 3, relay 304 disconnects the im pulse lead from the lower winding of magnet 35! and. transfers it to busy relay 3H3, whereby the latter relay is operated in the event that, for any reason, the call does not clear through the selector stage before the calling subscriber starts to dial the next digit.

B4. Generally preconditioning the secondary controllers At its armature 4, start relay 304 closes a point in the double-chain circuit (to be subsequently traced) to initiate the selecting and testing operations necessary to clear the .call through the selector stage. At'its armature I, start relay 304 grounds the associated common test-start conductor T-SI. This conductor is grounded by the start relay of any selector in any subgroup. Conductor T-ST extends to common test-start relay 8.70 (Fig. 8) which now operates toground conductors STA to STI in cables 'lII to H9 respectively, one for each secondary controller. Grounding of these conductors causes each idle secondary controller to prepare to test any of its associated outgoing trunks in preparation'for the extension of a connection over an idle one thereof.

If the secondary controller SCA (Fig. 8) is idle, both its group-controller relays so: and 9.02 are in restored condition. In this-event, the grounding of conductor STA in cable II I closes a circuit through the Winding of test-connecting relay -9-2I, by way of the back contacts 6 of relays 9M and 982 in series. Relay 92I thereupon operates, and connects the test conductors SI to SIS in cable 650 respectively to one terminal of the high-resistance test windings of relays TI to TI 5.

None of the relays TI to TI 5 of secondary controller SCA operates as the direct and immediate result of thedescribed operation of testconnecting relay 92!, as the other terminal of the test Winding the lower winding) of each of these relays is devoid of operating ground potential except as such potential is supplied through contacts of a grouping relay such as B5. The selector-subgroup chain Since the primary switches PA! to PAI5 with which the selectors SELAI-to SELAI5 are respectively associated are controlled. by the common selecting magnets52l to 532, the com mon selecting magnets must be placed under control of calling selectors only one at a time in order to avoid confusion. To this end, each selector is provided with a chain relay such as 305 of SEL-AI, and the chain relays of the fifteen selectors in a subgroup are interconnected in a local subgroup chain. Assuming the selector-subgroup-A chain to be idle( none of the chain relays such as 395 energized) at the time start relay 3M operates as previously described, the closure of contacts 4 of the latter relay extends ground potential, through contacts l of busy relay 383, to the common input conductor of register R380 by way of the following circuit path: from ground through the winding of relay (ill, chain-in conductor 3I2, back contact 4 of chain relay 395, the associated chain-out conductor CH OUT, through the corresponding chain contacts of the succeeding chain relays such as 385, the associated chainend conductor CH-END (being the chain-out conductor at the final selector SEL-AI5 of the subgroup), normally closed contacts controlled by armature 3 of chain relay 305, conductor C2 in selector multiple SMI, normally closed con-, tacts of stackup ON of switch PAI, conductor 'CI in selector multiple SMI, and thence, by way of contacts 4 of relays 304 and 303, to the input conductor common to contact pairs l to of the register R300.

The further extension of the above-noted ground potential at the moment depends upon whether the group controller (GCI, Fig. '7) associated with the called numerical group of trunks is busy or idle. If this group controller is busy, the ground potential in question is not operatively extended until the group controller becomes idle.

B6. The group-controller chain The disclosed arrangement is such that a group controller can be associated with only one primary subgroup at a time in order to avoid confusion in the completion of connections. For this purpose, all relays such as 40! associated with the same group controller are included in a chain opened by any operated one to indicate that the group controller is busy.

Assuming that group controller GCI is in idle condition at the moment, the above-noted extension of ground potential (by way of the windings of relays 4H and 305), to the input conductor common to contacts l to 0 of register R300 of the calling selector SAl, results in the closure of the following double-chain start circuit: from ground as previously traced to the common input conductor of register R300, and thence, through the closed contacts I of such register, over the selected dial lead DLl (common to selectors SEL-Al to SEL-Al5), the winding of numerical-group relay 431, the winding of group-controller relay 40 I, normally closed contacts controlled by armature 46 of relay 431, the associated common conductor CHEND (being the end conductor of the group controller chain), through series contacts of relays such as 40l associated with the succeeding selector subgroups, chain-out conductor CH-OUT of relay 40!, chain contacts 41 of relay 401, chainin conductor CI-I-IN in cable 42l, and thence through the winding of start relay to battery. Relays MI, 305, 43I, 4M, and 10! all operate in series over the above-traced circuit.

B7. Conditioning the selector links Relay 4| 1, at its armatures I to 20, applies an idle-indicating battery potential to each of the conductors SI to S20 in local cable 450, being the sleeve conductors S of the twenty selector links SL1 to SL20, respectively, extending from the associated primary subgroup A to the several secondary subgroups.

B8. Individualieing the primary subgroup with the calling selector Relay 305, at its armature 3, looks itself to conductor 312, at the same time disconnecting its winding from the associated conductor CH-END. At its armature 4, relay 305 disconnects conductor 3l2 from conductor CI-I-END (common to the fifteen selectors of the subgroup), thereby precluding operation of any further chain relays of the selector subgroup for the time being. That is, the subgroup chain is now busied to the remaining fourteen selectors. At its armatures l and 2, relay 305 connects the associated switching conductor 310 and busy conductor 3 respectively to the operate winding of hold magnet 50! and the winding of busy relay 303.

16 B9. Adapting the group controller according to the called numerical group Numerical-group relay 43I applies ground potential to conductor GI in cable 42l thereby operating grouping relays 84! and 851 (Fig. 8). Relay 04! connects the conductor pairs A to I of group controller GCI, Fig. '7 respectively to pairs IA to II in cables I l I to H9. This operation constitutes adaptation of the group controller GCI to direct the call under discussion to an idle trunk in the called numerical group I, as distinct from the other numerical groups (2 to 5) with which it can be adapted to operate by relays 842 to 845 respectively.

139a. Specifically conditioning the secondary controllers The stated operation of grouping relay 85] specifically conditions each idle secondary controller for operation in connection with the called numerical group I. It accomplishes this by applying ground potential to the upper terminal of the lower winding of each test relay in any secondary controller associated with a trunk line assigned to the called numerical group I. For example, at its contacts 2 and I, relay 05! grounds conductors AT! and AT2, thereby extending ground potential to the upper terminal of the lower winding of each of the test relays (Ti and T2) which are associated with trunks outgoing from secondary subgroup A and assigned to numerical group I. At such of its remaining contacts as are needed for the purpose, relay 85! similarly applies ground potential to one terminal of the lower winding of each test relay (not shown) in the other secondary controllers associated with outgoing trunks assigned to the called numerical group I. For convenience in altering assignment of the outgoing trunks to the numerical subgroups, conductors ATI to ITIS in cables III to H9 are brought to terminal blocks 86! to 869, whence any one of them can. be crossconnected to a contact pair of any one of the grouping relays 85l to 855, or to a contact pair of any one of the similar relays (not shown) controlled over conductors G6 to G0 (see Fig. 4) associated respectively with outgoing numerical groups 6 to 0.

As is shown in Fig. 1, the sleeve conductor S of each idle outgoing trunk is normally connected to an idle-indicating batter potential at the switching apparatus to which such trunk extends. Accordingly, the high-resistance lower winding of each of the trunk-test relays in each idle secondary subgroup (such as TI and T2, Fig. 9) which corresponds to an idle outgoing trunk in the called numerical group I is energized, operating the concerned test relay. If outgoing trunk CT! is idle, relay Tl has the following operating circuit: from ground through contacts 2 of grouping relay 85!, conductor ATI in cable III, the high resistance lower winding of relay Tl, contacts of the operated test-connecting relay 92L conductor SI in cable 650, normally closed makebusy contacts associated with off-normal contacts ON of secondary switch SAI. the operating winding of hold magnet 60!, and thence over sleeve conductor S of the outgoing trunk CT! to the above-noted source of idle-indicating battery potential. Magnet SM is not effectively energized by the closure of this circuit because of the abovenoted high resistance of the lower winding of relay TI ductors in. cable i2 I l5, it oonnects'the remaining conductorsl(MI:-to

If the'outgoing trunk assigned thereto is idle, test relay T2 (Fig. 9) operates over a circuit similar to that of relay TI. So does any test relay in the remaining secondary controllers which is associated with an idle trunk assigned to the called numerical group I.

From the foregoing, it will be seen that all idle secondar controllers are now specifically conditioned to assist in the completion of a call to the called numerical group'l. It wili be understood, of course, that all such secondary controllers can be contemporaneously specifically conditioned, by similar relay operations, to complete a call toany one or" the numerical groups 6 to 0, presided over by group controller G02. As will appear hereinafter, this causes no confusion, as the seizure of -a secondary controlle by either group controller excludes the other group controller therefrom .and causes the call to be completed according to the destination of the call being handled by the seizing group controller.

B10. Individualizing the group controller with the primar subgroup Relay Mil, at its armature 44,.1ooksitself to the associated chain-in conductor CI-I-.IN, at

the same time disconnecting its winding from the associatedconductor CH-END (commonto re- .laysiill in all selector subgroups). At its arh1ature 41, relay '40] opens the .chaincircuit bearmatures I andL-Z, rela fittconnectsithe subgroup busy and switching conductors 3H and 3 I I] .to conductorsBU and SW of cable i'ZLJeXtending to'group controller GC! (Fig. 7) ;.at its armature 3 itconnects primary ctr-normal lead PONin cable 456 withprimar off-normal lead: PON in 'cable 42I;.at itsarmaturese and it connects the local subgroup rmark. conductors MI-I Ii and M I I.2Il. respectively to the corresponding conwhile at its: armatures: 6. to

S) in local cable 559 to;respectiveconductors in cable 42!, extending to group controller GCI.

Conductors MI ito S253 of cable 455 :com-

'prise twentypairs, each pair being associated 'with a'separate one of the twenty links. extending: from the associated-primary subgroup A to the several secondary subgroups. Conductors MI and SI comprise the first pair (associated with the first link); M2 and S2 comprise the second pair; and soforth; toMZBand SEQ, which comprise the twentieth pair (associated with the twentieth link). It should be noted further that, as indicated most-clearly in-Fig. 7, cable 421 (and the same is true'for the similar cable l22) contains twenty-seven pairs of conductors IA, 2 A, and so forth, to tL each pair extending to a separate one of the twenty-seveniink-testrelays IA to-3I. A-separate combination of twenty of these test relays is used for each primarysubgroup. The particular combination used-for any primary subgroup is that combination which corresponds to the selector-link spread from that primary subgroup to the secondary subgroups, as: given in Table 2,-supra. Accordingly, at any selector subgroup, only twenty of the above-noted twenty-seven pairs of conductors IA to 31 in cable-2i are brought out to the contacts of the concerned connecting relay such -QI. Table 3, below, shows the particular combinationof the twenty seven pairs of conductors 18 in cable 42I which appears at the contacts of any relay such as 40L TABLE 3 B11. Preparing the group controller In group controller GCI (Fig. 7), when start relay 'HH operates as previously noted (in series with relays MI, 3. 35, MI, and 4M), it prepares a test circuit at its armature 2; at its armature I, it closes a circuit through contacts of test relay 102 for busy relay 1M. Relays H13 and 104 are both so designedand adjusted that neither has time to operate during the brief normal operation of the'group controller. "This intended 'operation'will 'be described subsequently.

Assuming'relays "H8" to I30 of the preference allotter tobe' in the respective conditions indicated (relays H8 and HI operated, the remaining restored), the operation of armature 3 of start relay IflI open-circuits relay H8 and closes an effective operating circuit for relay "H9. Relay H9 thereupon operates, but-without immediate effect. Relay 'll8'remains operated (to hold relay I2I operated) notwithstanding the fact that it is now-open-circuited,'for'it is a residualrelay (and the same'is true for relay 719) as is hereinafter described.

Blla. Setting the link-test relays As a resultof the connecting up'of the sleeve conductors S in the twenty pairs of conductors in cable s2I-Whichappear in .contactsofrelay MI, in accordance'with column A of the above Table 3, each concernedione ofthe link-test relays IA to 31 of the group controller GCI operates, subject to the selector link with which it is currently associated being idle. For example, if the first selector link-SLI extending from the concerned primary subgroup A, Fig. 5, is idle,

there is no groundjpotential on the'sleeve conductor thereof. Consequently, conductorSI in cable 450 is ungrounded. In this event, the'battery'potentiaL-placed on this conductor through the resistor associated with the front contact of armature I of relay 4| I passes effectively through the front contact of this armature to the said conductor and extends thence, through the operated armature i of relay liiI, and over conductor S in group IA of cable IEI, to the upper terminal of the winding of link-test relay IA in group controller GCI, providing an operating circuit for the said relay IA, whose lower terminal is grounded. On the other hand, if the selector link. in question is in use, a holding (and guarding) ground potential is maintained on the sleeve conductor S thereof, efiectively neutralizing the above-noted idle-indicating battery potential, in which event the said relay IA remains unoperated.

As will be seen from column A of Table 9, the twenty test relays of group controller GCI which are efiective in the present call (involving selector subgroup A and primary subgroup A) are relays IA to 3A, relays IE to 3B, relays IC and 20 (not shown), and so on, to relays II and 21. Each such relay is operated, or not (by a test connection similar to that for relay IA), depending upon whether the selector link with which the relay is currently associated is idle or busy.

If relay IA operates (indicating that the link with which it is currently associated is idle), at its armature I, it disconnects magnet conductor M of pair GCI-A in cable III from the corresponding armatures of the associated. relays 2A and 3A and transfers it to magnet conductor M in conductor pair IA in case 42 I, being the magnet conductor of the selector link with which the relay is currently associated. This is merely a preparatory operation, becoming effective only in case the link in question is selected, depending in turn upon whether there is an idle outgoing trunl: assigned to the called numerical group in secondary subgroup A, with which relays IA to 3A of the group controller are sociated.

B12. Path selection At its armature 2, relay IA prepares to ground switching conductor SW in cable MI, and at its armature 3 it connects the free terminal of the ground-connected test relay Hi2 to conductor IN in pair A of the group controller. This latter operation constitutes the testing operation determinative of which currently idle secondary subgroup in the order from A to I is the first subgroup containing the idle outgoing trunk assigned to the called numerical group, group I in the chosen example. With grouping relay 8M operated, conductor IN in pair A is connected, through contacts I of such relay, to conductor IN in pair IA of cable III. This latter conductor extends to the upper armature of test relay TI in secondary controller SCA, for relay TI is associated with trunk OTI (Figs. .2 and 6) outgoing from secondary subgroup A and assigned to the called numerical group i. In the illustrative wiring of secondary controller SCA,

the first two trunks outgoing from secondary subgroup A are assigned to the first numerical group, the second two trunks to the second numerical group, and so on, to the fifth pair of trunks which are assigned to the fifth numerical group, the remaining five trunks outgoing from this secondary subgroup being assigned respectively to numerical groups 6 to 0.

If the two outgoing trunks in secondary subgroup A assigned to the currently called nu merical group I are both in use, trunk-test relays TI and T2 are both in restored condition, as hereinbefore explained. In this event, the ground potential applied (by way of the winding of test relay "I02 and contacts of the operated relays IIII, "HE, HI, IA, and BM) to conductor IN in pair IA in cable II I, is extended, through back contacts of the upper armatures of relays TI and T2, and thence over the associated conductor OUT, contacts 2 of grouping relay MI, and conductors OUT of pair A, to armature 3 of relay IB, whereby secondary subgroup A is by-passed, and the control over trunk selection is transferred to secondary subgroup B, through which it may be transferred in a similar manner to any one of the succeeding secondary subgroups, to become effective at the first point where there is an idle selector link outgoing from the calling primary subgroup to an idle secondary subgroup containing an idle trunk assigned to the called numerical group.

Bl2a. Selecting secondary controller SC'A With link-test relay IA operated as assumed, if either of test relays TI and T2 is in operated condition (indicating an idle outgoing trunk leading from secondary subgroup A, to the called numerical group), incoming conductor IN in pair IA of cable III is disconnected from outgoing conductor OUT of the same pair, and a selecting circuit is completed locally in the secondary controller SCA, through the upper winding of one or another of the relays TI and T2.

If relay TI is energized (by its high-resistance lower winding), the previously described operation of relay IA completes the following selecting circuit: from ground through the winding of testrelay I02, contacts 2 of start relay IIII, front contact of armature I of relay H8, front contact of armature 2 of relay I34, front contact of armature 3 of relay IA, conductor IN of pair A, contacts I of relay 8, conductor IN in group IA of cable II I, front contact of the upper armature of trunk-test relay TI, the upper winding of relay TI, conductor I in cable 900, groupcontroller relay 9III, and thence to battery through the back contact of armature 6 of relay 902. The closure of this circuit establishes a holding current through the'upper winding of relay TI, and an operating current for test relay I62 and group-controller relay 89L Test relay I02 disconnects busy relay I04, and substitutes busy relay I03 for a purpose to be subsequently made clear.

with. the group controller Relay SUI opens the chain circuit of test-connecting relay 92I at its contacts 6. When this occurs, relay 92I restores and disconnects the lower windings of the fifteen trunk-test relays TI to TIE, whereupon any operated one of these relays restores, with the exception of relay TI, which is held by current flow through its upper winding over the above-traced circuit. Restoration of these relays operates to mark the secondary controller SCA (and consequently the corresponding secondary subgroup A of switches) as busy to the group controllers G02, Fig. 2. This is done by joining incoming test conductor IN to outgoing test conductor OUT in each of the groups 6A to DA in cable III. Secondary controller SCA is now individualized with group controller GCI.

As a further result of its described operation, group-controller relay 9IlI causes connection to 

